jtag: usb_blaster: fix allocation of usb_blaster_device_desc

usb_blaster_device_desc was allocated, but never freed.

Change-Id: I764bd092c71b8c260b98aab0e7a1710fd7bfa9fd
Signed-off-by: Stefan Mahr <stefan.mahr@sphairon.com>
Reviewed-on: http://openocd.zylin.com/1224
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Tested-by: jenkins

src/jtag/drivers/usb_blaster.c

@@ -338,7 +338,7 @@ static int usb_blaster_init(void)
 	if (usb_blaster_device_desc == NULL) {
 		LOG_WARNING("no usb_blaster device description specified, "
 			"using default 'USB-Blaster'");
-		usb_blaster_device_desc = "USB-Blaster";
+		usb_blaster_device_desc = strdup("USB-Blaster");
 	}
 
 #if IS_WIN32 == 0
@@ -469,6 +469,11 @@ static int usb_blaster_quit(void)
 	ftdi_deinit(&ftdic);
 #endif
 
+	if (usb_blaster_device_desc) {
+		free(usb_blaster_device_desc);
+		usb_blaster_device_desc = NULL;
+	}
+
 	return ERROR_OK;
 }